Controller for optical transmission device

Abstract

A controller supplies a driving signal to an optical modulator for modulating light from a light source in accordance with the driving signal, a low frequency signal being superposed on the driving signal. A bias unit monitors a low frequency component of the modulated light and controls bias of the optical modulator. A compensation unit controls the intensity of the light so as to compensate for refractive index variation of the optical modulator which is caused by variation of the bias.

1 . A controller comprising:
 a signal supplier for supplying a driving signal to an optical modulator for modulating light from a light source in accordance with the driving signal, a low frequency signal being superposed on the driving signal;   a bias unit for monitoring a low frequency component of the modulated light and controlling bias of the optical modulator; and   a compensation unit for controlling the intensity of the light so as to compensate for refractive index variation of the optical modulator which is caused by variation of the bias.   
   
   
       2 . The controller according to  claim 1 , wherein the compensation unit controls driving power of the light source to compensate for the refractive index variation of the optical modulator. 
   
   
       3 . The controller according to  claim 1 , wherein the compensation unit controls an attenuation amount of an optical attenuator for attenuating the modulated light to compensate for the refractive index variation of the optical modulator. 
   
   
       4 . The controller described in any one of  claims 1  to  3 , wherein the compensation unit calculates a variation amount of refractive index of the optical modulator to the variation amount of the bias, and compensates the refractive index variation on the basis of the calculated variation amount. 
   
   
       5 . A control method of an optical transmitter having an optical modulator for modulating light from a light source in accordance with a driving signal on which a low-frequency component is superposed, comprising:
 supplying the driving signal to the optical modulator;   monitoring a low frequency component of the modulated light to control bias of the optical modulator; and   controlling the intensity of the light so as to compensate for refractive index variation of the optical modulator which is caused by variation of the bias.   
   
   
       6 . The control method according to  claim 5 , wherein the refractive index variation of the optical modulator is compensated by controlling driving power of the light source. 
   
   
       7 . The control method according to  claim 5 , wherein the refractive index variation of the optical modulator is compensated by controlling an attenuation amount of an optical attenuator for attenuating the modulated light. 
   
   
       8 . The control method according to  claim 5 , wherein a variation amount of refractive index of the optical modulator to the variation amount of the bias is calculated, and the refractive index variation is compensated on the basis of the calculated variation amount. 
   
   
       9 . An optical transmission device, comprising:
 a light source;   an optical modulator for modulating light from the light source; and   a controller for controlling the light source and the optical modulator; wherein,   the controller comprises:
 a signal supplier for supplying a driving signal to an optical modulator for modulating light from a light source in accordance with the driving signal, a low frequency signal being superposed on the driving signal; 
 a bias unit for monitoring a low frequency component of the modulated light and controlling bias voltage of the optical modulator; and 
 a compensation unit for controlling the intensity of the light source so as to compensate for refractive index variation of the optical modulator which is caused by variation of the bias. 
   
   
   
       10 . An optical transmission device, comprising:
 an optical modulator for modulating light from a light source;   an optical attenuator for attenuating light modulated in the optical modulator; and   a controller for controlling the optical modulator and the optical attenuator, wherein, the controller comprises:   a signal supplier for supplying a driving signal to an optical modulator for modulating light from a light source in accordance with the driving signal, a low frequency signal being superposed on the driving signal;   a bias unit for monitoring a low frequency signal of the modulated light and controlling bias voltage of the optical modulator; and   a compensation unit for controlling an attenuation amount of the optical attenuator so as to compensate for refractive index variation of the optical modulator which is caused by variation of the bias.